Controlling charge flow in the electrical stimulation of tissue

ABSTRACT

Systems of techniques for controlling charge flow during the electrical stimulation of tissue. In one aspect, a method includes receiving a charge setting describing an amount of charge that is to flow during a stimulation pulse that electrically stimulates a tissue, and generating and delivering the stimulation pulse in a manner such that an amount of charge delivered to the tissue during the stimulation pulse accords with the charge setting.

BACKGROUND

This disclosure relates to controlling the flow of charge in theelectrical stimulation of tissue.

Tissues can be electrically stimulated directly or indirectly to elicita desired response. Direct stimulation involves the provision of one ormore electrical stimuli directly to the stimulated tissue. Indirectstimulation involves the provision of one or more electrical stimuli toadjacent or otherwise related tissue, where the related tissue causesthe desired response to be elicited from the stimulated tissue. Thedesired response can be, e.g., inhibitory or excitatory. Inhibitoryresponses tend to discourage certain behavior by the stimulated tissue,whereas excitatory responses tend to encourage certain behavior by thestimulated tissue. Encouraged or discouraged behaviors can includecellular depolarization, the release of chemical species, and/or theinhibition of cellular depolarization.

Electrical stimuli can be used by medical devices to stimulate tissue ina number of different settings, including therapeutic, diagnostic, andfunctional settings. In such settings, electrical stimulation often isprovided in accordance with stimulation parameters. The stimulationparameters characterize the electrical stimuli for purposes of delivery.

SUMMARY

Systems and techniques relating to controlling charge flow in theelectrical stimulation of tissue are described. In one aspect, a methodincludes receiving a charge setting describing an amount of charge thatis to flow during a stimulation pulse that electrically stimulates atissue, and generating and delivering the stimulation pulse in a mannersuch that an amount of charge delivered to the tissue during thestimulation pulse accords with the charge setting.

This and other aspects can include one or more of the followingfeatures. A stimulation waveform that includes the stimulation pulse anda secondary pulse can be generated. The secondary pulse can reduceaccumulation of charge at an electrode that has delivered thestimulation pulse. The charge setting can be received from a user. Thedelivery of the stimulation pulse can include monitoring the flow ofcharge during delivery of the stimulation pulse, and halting thedelivery based on the amount of charge described by the charge setting.The delivery can be halted based on the flow of charge exceeding theamount of charge described by the charge setting.

The delivery of the stimulation pulse can include changing, based on thecharge setting, one or more stimulation parameters that characterize oneor more aspects of a stimulation waveform that includes the stimulationpulse, and delivering the stimulation waveform in accordance with thestimulation parameters. The stimulation parameters can be changed byconverting the charge setting into the one or more stimulationparameters. The charge setting can be converted by calculating astimulation pulse duration using a stimulation pulse amplitude or byaccessing a data compilation using the charge setting to identify atleast one of a predetermined stimulation pulse duration and apredetermined stimulation pulse amplitude. The charge setting can alsobe converted by holding a stimulation pulse amplitude substantiallyconstant for two or more different charge settings and determining astimulation pulse duration based on the received charge setting and thesubstantially constant stimulation pulse amplitude. Holding thestimulation pulse amplitude substantially constant can include accessinga data compilation that associates a substantially constant stimulationpulse amplitude with the two or more charge settings.

The charge setting can also be converted into the one or morestimulation parameters by holding a stimulation pulse durationsubstantially constant for another two or more different chargesettings, and determining a stimulation pulse amplitude based on thereceived charge setting and the substantially constant stimulation pulseduration. The settings for which stimulation pulse amplitude is heldsubstantially constant can be discrete charge settings that describerelatively smaller amounts of charge flow. The charge settings for whichstimulation pulse duration is held substantially constant can bediscrete charge settings that describe relatively larger amounts ofcharge flow. There can be no charge settings intermediate between thecharge settings for which stimulation pulse amplitude is heldsubstantially constant and the charge settings for which stimulationpulse duration is held substantially constant. Holding the stimulationpulse amplitude substantially constant can include accessing a datacompilation that associates each of a plurality of substantiallyconstant voltage steps with two or more charge settings.

In another aspect, a method includes receiving a charge boundarydescribing a largest amount of charge that is to flow in a stimulationpulse of an electrical stimulation waveform, receiving a change to thestimulation waveform, determining that the received change to thestimulation waveform would cause the stimulation pulse to violate thecharge boundary, and accommodating the change to the stimulationwaveform based on the determination. The stimulation pulse is toelectrically stimulate tissue when delivered over an electrode.

This and other aspects can include one or more of the followingfeatures. A charge setting describing a proposed amount of charge to bedelivered in the stimulation pulse can be received. The charge boundarycan be compared to the received charge setting to determine that thereceived change to the stimulation waveform would cause the stimulationpulse to violate the charge boundary. The change to the stimulationwaveform can be received at an extracorporeal portion of a system thatincludes an implanted stimulator.

The accommodation of the change to the stimulation waveform can includerejecting the change to the stimulation waveform or changing thestimulation waveform so that the amount of charge to flow in thestimulation pulse accords with the amount of charge identified by thecharge boundary. The stimulation waveform can be changed by convertingthe charge boundary into one or more stimulation parameters or byhalting a stimulation pulse when the amount of charge does not accordwith the amount of charge described by the charge boundary. The changeto a stimulation waveform can be received when the waveform is activelybeing delivered to electrically stimulate the tissue.

In another aspect, a system includes a user interface configured tointeract with a user to receive a charge setting describing an amount ofcharge that is to flow in the electrical stimulation of tissue, aconverter configured to convert the received charge setting into one ormore stimulation parameters, the stimulation parameters characterizingaspects of a stimulation waveform that is to be delivered to stimulatethe tissue, a signal generator that is programmable to generate thestimulation waveform in accordance with the stimulation parameters, andan electrode arranged to receive the stimulation waveform from thesignal generator and to deliver the stimulation waveform to stimulatethe tissue.

This and other aspects can include one or more of the followingfeatures. The system can include an implantable stimulator that includesthe signal generator and the electrode. The implantable stimulator caninclude the converter. The converter can be a data processing deviceconfigured to perform at least a portion of the conversion of the chargesetting in accordance with logic of a set of machine-readableinstructions.

The converter can include a memory device that associates individualcharge settings with collections of the changes to the stimulationparameters and/or special purpose logic circuitry to perform at least aportion of the conversion. The user interface can be configured toreceive a first charge setting that specifies a relative change in theamount of charge that is to flow in the electrical stimulation of tissueor to receive a first charge setting that directly specifies the amountof charge that is to flow in the electrical stimulation of tissue.

The user interface can also be configured to receive a first chargesetting that identifies an incremental increase or a decrementaldecrease in the amount of charge that is to flow in the electricalstimulation of tissue. The user interface can be configured to interactwith a user to receive a charge boundary describing a largest amount ofcharge that is to flow in a stimulation pulse for the electricalstimulation of tissue.

The system can also include a comparator to compare the one or morestimulation parameters with the charge boundary to ensure that thestimulation waveform would not violate the charge boundary. Thecomparator can compare the charge setting with the charge boundary toensure that the stimulation waveform would not violate the chargeboundary.

In another aspect, a system for controlling charge flow duringelectrical stimulation of tissue includes a waveform generatorconfigured to generate a waveform to electrically stimulate the tissue,a receiver configured to receive a charge setting specifying an amountof charge to be delivered in the electrical stimulation of tissue, and acoulomb counter configured and arranged to measure an amount of chargedelivered in a stimulation pulse and to generate the trigger when theamount of charge delivered accords with that specified by the chargesetting. The waveform generator is programmable to end the generation ofa stimulation pulse based on receipt of a trigger. The waveformgenerator includes a trigger input to receive the trigger. The coulombcounter includes a trigger output to convey the trigger to the triggerinput of the programmable waveform generator.

This and other aspects can include one or more of the followingfeatures. The system can include an implantable stimulator that includesthe waveform generator and the coulomb counter. The implantablestimulator can also include the receiver. The receiver can be a wirelessdata receiver configured to receive a wireless signal that includes thecharge setting. The receiver can include an extracorporeal userinterface configured to receive the charge setting from a human user.The system can also include step-up circuitry configured to increase avoltage for the stimulation pulse above a supply voltage of the waveformgenerator.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features andadvantages will be apparent from the description, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a system in which charge flow during stimulation can becontrolled.

FIG. 2 shows one implementation of an implanted portion of the system ofFIG. 1.

FIG. 3 shows example stimulation parameters that characterize a stimuluswaveform.

FIG. 4 shows one implementation of a housing of the external portion ofthe system of FIG. 1.

FIG. 5 is a flowchart of a process by which the flow of charge duringthe electrical stimulation of tissue can be controlled.

FIG. 6 shows an implementation of the stimulator of FIG. 2 in whichcharge flow during stimulation can be controlled.

FIGS. 7 and 8 are flowcharts of processes by which the flow of chargeduring the electrical stimulation of tissue can be controlled.

FIG. 9 shows a block diagram of circuitry that can convert a chargesetting into a stimulation parameter.

FIG. 10 shows a process for the conversion of a charge setting into astimulation parameter.

FIGS. 11 and 12 show data compilations for use in the conversion of acharge setting into a stimulation parameter.

FIG. 13 shows a trip duration and a trip amplitude on the waveform ofFIG. 3.

FIGS. 14 and 15 show processes for controlling charge flow during theelectrical stimulation of tissue.

FIG. 16 shows a block diagram of the stimulator of FIG. 2 in whichcharge flow is controlled during stimulation.

FIG. 17 shows a data compilation for use in the conversion of a chargesetting into a stimulation parameter.

FIGS. 18, 19, and 20 show another implementation of an implanted portionof the system of FIG. 1.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 shows a system 100 in which charge flow during stimulation can becontrolled. System 100 can include an implanted portion 105 and anexternal (i.e., extracorporeal) portion 110. Implanted portion 105 is adevice that is adapted for implantation in a body. For example,implanted portion 105 can include a biocompatible housing adapted toreduce the immune response and/or cell necrosis associated with theimplantation of portion 105. Implanted portion 105 can stimulate tissue.For example, implanted portion 105 can electrically excite thedepolarization of a nerve and/or muscle tissue for therapeutic,diagnostic, and/or functional purposes. As discussed further below,implanted portion 105 can include one or more elements to deliverelectrical stimuli to tissue.

In some implementations, implanted portion 105 can be implanted in abody with one or more surgical insertion tools tailored for theimplantation of portion 105. Alternatively, implanted portion 105 can beimplanted using commercially available surgical equipment, such ashypodermic needles, conventional surgical equipment, and endoscopic orlaparoscopic devices.

In some implementations, implanted portion 105 can operate independently(i.e., as a solitary implanted device) or implanted portion 105 canoperate as part of an implanted system of devices whose activities arecoordinated to achieve therapeutic, diagnostic, and/or functionalpurposes.

In some implementations, implanted portion 105 can receive data from oneor more sensing devices (not shown) that respond to one or moreconditions of the body in which implanted portion 105 is implanted.Example sensing devices include chemical sensors, electrodes, opticalsensors, mechanical (e.g., motion, pressure) sensors, and temperaturesensors. The received data can be used by implanted portion 105 incontrolling the electrical stimulation of tissue.

External (extracorporeal) portion 110 is a device for providing userinteraction with implanted portion 105. External portion 110 isgenerally situated outside the body in which implanted portion 105 isimplanted. External portion 110 can include a user interface 115, a datatransceiver 120, a power transmitter 125, a processor 130, and a memory135. User interface 115, data transceiver 120, power transmitter 125,processor 130, and memory 135 can be housed in a single housing or inmultiple housings. User interface 115, data transceiver 120, powertransmitter 125, processor 130, and memory 135 can be linked for datacommunication and control by one or more wired (e.g., wires, busses,optical fiber) or wireless (e.g., infrared, WiFi, sound, magnetic,electromagnetic, radio frequency (RF)) data links.

User interface 115 can include one or more input/output devices forinteracting with a user. For example, input/output devices can bemechanical, audio, and/or visual devices, including keypads, touch- anddisplay-screens, speakers, and data ports.

Data transceiver 120 communicates with implanted portion 105 over a datalink 140. This communication can include both the transmission andreception of data, including data that represents commands received froma user over user interface 115 and data regarding the operational statusand history of implanted portion 105. For example, data that representsa charge setting, a charge boundary, boundaries on stimulationparameters, the current operational settings of stimulation parameters,and whether or not implanted portion 110 is actively stimulating tissuecan be communicated over data link 140.

Data transceiver 120 includes both a transmitter and a receiver. Datatransceiver 120 can be a wireless transceiver in that transceiver 120communicates with implanted portion 105 without the use of a transdermalphysical link. For example, data transceiver 120 can communicate withimplanted portion 105 using sound and/or electromagnetic radiation(e.g., light or radio waves) that propagates through a body to and fromimplanted portion 105.

Power transmitter 125 relays energy to implanted portion 105 over apower link 145. The energy relayed from transmitter 125 can be capturedand stored in implanted portion 105 and subsequently converted into oneor more stimuli for stimulating tissue. The relayed energy can includeelectrical energy, magnetic energy, electromagnetic energy, and/ormechanical energy. Power transmitter 125 can be a wireless transmitterin that transmitter 125 relays energy to implanted portion 105 withoutthe use of a transdermal physical link.

Processor 130 is a data processing device that performs processingactivities in accordance with logic established by a set ofinstructions. The logic can be embodied in hardware and/or software. Forexample, the processor 130 can be a microprocessor, ASIC's, FPGA's,and/or a set of logic elements arranged to embody the logic.

The logic of processor 130 can implement operations associated withcontrolling the electrical stimulation of tissue. These operations caninclude the management of interactions with a user over user interface115, the communication of data with implanted portion 105 over datatransceiver 120, and the relaying of energy to implanted portion 105over power transmitter 125. These operations can also include variousprocesses described below.

Memory 135 is a storage device that can store instructions and/or datafor controlling the stimulation of tissue in machine-readable format.Memory 135 can be accessed by one or more of user interface 115, datatransceiver 120, power transmitter 125, and processor 130 to storeand/or retrieve instructions and/or data. Memory 135 can include amemory controller or other interface to facilitate such exchanges ofinformation.

FIG. 2 shows one implementation of implanted portion 105, namely anelectrical stimulator 200. Stimulator 200 includes a pair of electrodes205, 207 mounted on a narrow, elongate capsule 212. The outer surface216 of capsule 212 can be made, at least in part, of a biocompatiblematerial such as biocompatible polymers, glasses, metals, and/or otherceramics. Capsule 212 can be sealed to exclude water but permit passageof electromagnetic fields used to transmit data and/or power.

In various implementations, capsule 212 can have a diameter of less thanabout 4-5 mm, or less than about 3.5 mm. Similarly, capsule 212 can havea length of less than about 30-40 mm, less than about 20-30 mm, or lessthan about 20 mm. The shape of the capsule 212 can be tailored to thedesired target, the surrounding area, and the method of surgicalinsertion. Shapes other than the thin, elongated cylinder withelectrodes at the ends as shown in FIG. 2, such as disks, helical,asymmetrical, or ovoid structures, are possible.

Each electrode 205, 207 traverses the wall of capsule 212 at arespective of openings 217, 219. Electrode 205 can be a stimulatingelectrode that electrically stimulates tissue, and electrode 207 can bean indifferent electrode that completes the electrical circuit for thestimulating waveform. Electrodes 205, 207 can be made of a conductingceramic, conducting polymer, and/or a noble or refractory metal, such asgold, silver, platinum, iridium, tantalum, titanium, niobium or theiralloys that minimize corrosion, electrolysis, and damage the surroundingtissues.

Capsule 212 houses electronic circuitry 210, a data transceiver 215, anda power source 220. Electronic circuitry 210 can control and/or performoperations in stimulator 200, including the receipt of data and/orpower, the decoding and storing data, the generation of electricalstimulation pulses, as well as all or portions of the processesdescribed below.

Electronic circuitry 210 includes a memory 225 and is connected toelectrodes 205, 207 by electrical leads 227, 229. Memory 225 is astorage device that can store instructions and/or data for controllingthe stimulation of tissue. Electrical leads 227, 229 can be short,flexible leads. For example, leads can be shorter than about 100-150 mm.

Data transceiver 215 includes both a transmitter and a receiver totransmit and receive data from outside of stimulator 200. For example,transceiver 215 can communicate over data link 140 with data transceiver120 in external portion 110 (FIG. 1).

Power source 220 can supply and store electrical energy for use bystimulator 200. Power source 220 can include a power storage device suchas battery or capacitor. Power source 220 can also include a powerreceiver portion that receives power from outside of stimulator 200,such as an RF link. For example, power source 220 can receive powertransmitted over power link 145 from power transmitted 125 in externalportion 110 (FIG. 1).

In one implementation of stimulator 200, stimulator 200 is able togenerate:

anodic stimulation pulses and cathodic secondary pulses;

a maximum cathodic current of 30 mA, a maximum cathodic current of 8 mA,or a maximum cathodic current of 3 mA;

a maximum cathodic compliance voltage of 30 V, a maximum cathodiccompliance voltage of 12 V, or a maximal cathodic compliance voltage of3 V;

a maximum anodic current of 10 mA, a maximum anodic current of 5 mA, ora maximum anodic current of 0.5 mA;

a maximum anodic compliance voltage of 10 V, a maximum anodic compliancevoltage of 5 V, or a maximal anodic compliance voltage of 1 V;

cathodic and anodic pulse widths of between 0.05 and 10.0 msec, pulsewidths of between 0.05 and 2.0 msec, or pulse widths of between 0.1 and0.5 msec; and

a stimulation frequency of between 1 and 200 pulses/second, or astimulation frequency of between 5 and 50 pulses/second.

In other implementations, stimulator 200 can generate pulses withstimulation parameters outside these ranges. In other implementations,stimulator 200 can generate cathodic stimulation pulses and anodicsecondary pulses with corresponding characteristics.

Other configurations of stimulator 200 are possible. For example,stimulator 200 can be a BION® microstimulator (Advanced Bionics®Corporation, Valencia, Calif.). Various details associated with themanufacture, operation, and use of BION implantable microstimulators aredescribed in U.S. Pat. Nos. 5,193,539, 5,193,540, 5,312,439, 6,185,452,6,164,284, 6,208,894, and 6,051,017, the contents of all of which areincorporated herein by reference.

In other implementations, stimulator 200 can include an implantablepulse generator (IPG) coupled to a lead of electrodes, a spinal cordstimulator (SCS), a cochlear implant, a deep brain stimulator, or anyother type of implantable stimulator configured to deliver electricalstimuli. Example IPG's include those described in U.S. Pat. Nos.6,381,496, 6,553,263, and 6,760,626, the contents of all of which areincorporated herein by reference.

Example spinal cord stimulators include those described in U.S. Pat.Nos. 5,501,703, 6,487,446, and 6,516,227, the contents of all of whichare incorporated herein by reference. Example cochlear implants includethose described in U.S. Pat. Nos. 6,219,580, 6,272,382, and 6,308,101,the contents of all of which are incorporated herein by reference.Example deep brain stimulators include those described in U.S. Pat. Nos.5,938,688, 6,016,449, and 6,539,263, the contents of all of which areincorporated herein by reference.

FIG. 3 shows example stimulation parameters that characterize a stimuluswaveform 300. Stimulus waveform 300 is an electrical signal thatstimulates tissue. For example, waveform 300 can electrically excite thedepolarization of a nerve and/or muscle tissue. Stimulus waveform 300can be delivered by one or more electrodes in implanted portion 105.

Stimulus waveform 300 can represent either the voltage or the current ofelectrical stimuli as a function of time T. Stimulus waveform 300 can bea balanced-charge biphasic waveform in that substantial charge does notaccumulate at the interface of an electrode that delivers stimuluswaveform 300 and electrode corrosion is maintained at an acceptablelevel. In one implementation, stimulus waveform 300 includes arepetitive series of alternating primary stimulation pulses 305 andsecondary recovery pulses 310. Primary stimulation pulses 305 areelectrical transients that are adapted to stimulate tissue. Secondaryrecovery pulses 310 are electrical transients that are adapted to reducethe accumulation of charge at the electrode interface due to primarystimulation pulses 305.

In the illustrated implementation, stimulus waveform 300 ischaracterized by a primary pulse amplitude parameter 315, a primarypulse duration parameter 320, a delay parameter 325, a secondary pulseamplitude parameter 330, a secondary pulse duration parameter 335, aperiod parameter 340, and a pulse shape parameter 345.

Primary pulse amplitude parameter 315 characterizes either the voltageor current pulse amplitude of primary stimulation pulses 305 in waveform300, whereas primary pulse duration parameter 320 characterizes theduration of primary stimulation pulses 305. Primary pulse amplitudeparameter 315 is generally given in units of voltage or current, whereasprimary pulse duration parameter 320 is generally given in units oftime.

Delay parameter 325 characterizes the time between a primary pulse 305and a secondary pulse 310. The time characterized by delay parameter 325is generally long enough to prevent secondary pulses 310 frominterfering with the stimulation of tissue by primary pulses 305.

Secondary pulse amplitude parameter 330 characterizes either the voltageor current pulse amplitude of secondary recovery pulses 310 in waveform300, whereas secondary pulse duration parameter 335 characterizes theduration of secondary recovery pulses 310. Secondary pulse amplitudeparameter 330 is generally given in units of voltage or current, whereassecondary pulse duration parameter 335 is generally given in units oftime.

Period parameter 340 characterizes the time between repetitions ofidentical portions of stimulus waveform 300. As illustrated, periodparameter 340 characterizes the time between successive primary pulses305 in waveform 300. Period parameter 340 can also be expressed as apulse rate (e.g., pulses per time). Pulse shape parameter 345characterizes an aspect of one or more pulses in waveform 300. Asillustrated, pulse shape parameter 345 characterizes the rising slope ofprimary pulses 305, but a variety of other pulses and other aspects ofpulses can be characterized by pulse shape parameters.

Stimulus waveform 300 can be tailored to stimulate specific cellpopulations and exclude others from stimulation. For example, relativelylow frequency electrical stimulation (e.g., less than about 50-100 Hz)may have an excitatory effect on an adjacent neural cell, leading toincreased neural activity, whereas relatively high frequency electricalstimulation (e.g., greater than about 50-100 Hz) may have an inhibitoryeffect, leading to decreased neural activity. Similar tailoring can beused to stimulate and exclude other classes of tissues, such as muscletissue.

FIG. 4 shows one implementation of a housing of external portion 110,namely a housing 400. Housing 400 is adapted to shelter certainsensitive components of user interface 115, data transceiver 120, powertransmitter 125, processor 130, and memory 135 from the environmentwhile allowing a user to interact with other, less sensitive components.

One collection of components with which a user can interact is acollection of charge setting components 405. Charge setting components405 interact with a user to allow a user to set the charge delivered bystimulation pulses, such as stimulation pulses 305 in waveform 300 (FIG.3). Charge is a quantity of electricity and charge delivery in astimulation pulse is generally the result of the introduction orwithdrawal of electrons during the stimulation pulse. Charge can bemeasured in Coulombs or in other units that can be converted intoCoulombs.

The amount of charge actually delivered in a stimulation pulse isrelated to the characteristics of the stimulation pulse. For example,when primary pulse amplitude parameter 315 characterizes the currentamplitude of primary stimulation pulses 305 in waveform 300, the amountof charge actually delivered (Q) can be approximated by:Q≈(pulse amplitude 315)(pulse duration 320).  Equation 1Equation 1 can adjusted to accommodate various forms of pulse amplitude315. For example, when pulse amplitude 315 changes over time, Equation 1can be changed to a time integral that includes the changing pulseamplitude 315.

On the other hand, when primary pulse amplitude parameter 315characterizes the voltage amplitude of primary stimulation pulses 305 inwaveform 300, the amount of charge delivered (Q) depends on theimpedance of the stimulating electrode/body interface (Z) and can beapproximated by:Q≈(pulse amplitude 315)(pulse duration 320)/(Z).  Equation 2The impedance Z can be determined repeatedly during the operation of astimulator. Alternatively, the impedance Z can be estimated andprogrammed into the stimulator and/or external portion. Equation 2 canbe adjusted to accommodate various forms of pulse amplitude 315 andimpedance Z. For example, when pulse amplitude 315 and/or impedance Zchanges over time, Equation 2 can be changed to a time integral thatincludes the changing pulse amplitude 315 and/or impedance Z.

The impedance Z refers to the electrical impedance of current flow fromone electrode through tissue and into another electrode. Electricalimpedance can vary over time with changes in the electrodes and/orsurrounding tissue. For example, the location of an electrode within amoving body can vary over time, the electrical characteristics of tissueat the site of stimulation can vary over time, or the electrode canbecome contaminated (e.g., biofouling) or otherwise change over time.

The collection of charge setting components 405 includes an outputelement 410 and input elements 415. Output element 410 is a device thatconveys information to a user. Output element 410 can convey information(such as a current charge setting and proposed changes to the chargesetting) visually. For example, output element 410 can be an LCD, amechanical display, and/or an LED display. Output element 410 can alsoconvey information non-visually. For example, output element 410 can bea speaker or a vibrating element.

Input elements 415 are devices that receive information from a user.Input elements 415 can receive information (such as changes to thecharge setting) mechanically. For example, input elements 415 can be apair of pushbuttons 420, 425. Pushbutton 420 allows a user to increase acharge setting by an incremental step. Pushbutton 425 allows a user todecrease a charge setting by an decremental step.

After receipt, a charge setting can be stored and/or inspected todetermine if the charge setting is appropriate. Determining if a chargesetting is appropriate can include comparing the charge setting with oneor more charge setting boundary values. A charge setting boundary valuecan be the highest or lowest allowable and/or possible value of a chargesetting. A charge setting boundary value can reflect the technicalcharacteristics of the stimulating device or a charge setting boundaryvalue can be set by a physician or other medical personnel in light ofthe placement of the stimulator, the purpose of the stimulation, and/orthe characteristics of the stimulator (e.g., to reduce corrosion to anacceptable level). For example, a charge setting boundary value can bereceived over a user interface such as charge setting components 405(FIG. 4).

FIG. 5 is a flowchart of a process 500 by which the flow of chargeduring the electrical stimulation of tissue can be controlled. Process500 can be performed, e.g., by a system for electrically stimulatingtissue, such as system 100 (FIG. 1).

The system performing process 500 receives a charge setting at anexternal portion at 505. The received charge setting can be a change inthe charge setting (e.g., an incremental or decremental change) or thereceived charge setting can be a new value of the charge setting. Forexample, when process 500 is performed by a system such as system 100,the charge setting can be received over input elements 415 of housing400 of external portion 110 (FIG. 4).

The received charge setting can be transmitted to a stimulator at 510.For example, the charge setting can be transmitted by a data transceiver120 over a data link 140 to a data transceiver 215 of an implantedstimulator 200 (FIGS. 1 and 2).

The stimulator receives the charge setting at 515 and stores the chargesetting at 520. For example, a charge setting can be received byreceiver 215 and stored in a memory such as memory 315 of implantedstimulator 200 (FIG. 2).

The stimulator can stimulate in accordance with the charge setting at525. Stimulating in accordance with the charge setting includesattempting to ensure that the amount of charge specified by the chargesetting is actually introduced or withdrawn during a stimulation pulse.

FIG. 6 shows an implementation of a stimulator 200 in which charge flowduring stimulation can be controlled. Stimulator 200 includes electrodes205, 207, receiver 215, leads 229, 227, and electrical circuitry 210.Electrical circuitry 210 includes a waveform generator 605 and a coulombcounter 610. Waveform generator 605 generates a stimulation waveform tostimulate tissue. Waveform generator 605 is connected to electrodes 205,207 by leads 229, 227 to deliver the stimulation waveform. Electrodes205, 207 and leads 229, 227 can be electrodes and leads in any systemfor electrically stimulating tissue. Waveform generator 605 is aprogrammable waveform generator. For example, in one implementation, theend of a stimulation pulse output by generator 605 can be triggered byan end input received over a control line 615.

Coulomb counter 610 is a device that measures the delivery of charge byelectrodes 205, 207 during a stimulation pulse. Coulomb counter 610 canoperate, e.g., by measuring a voltage drop across a low impedance seriesresistance on one or both of leads 229, 227. Coulomb counter 610 is indirect or indirect data communication with receiver 215 over a data path620. Data path 620 is capable of relaying a charge setting received atreceiver 215 to coulomb counter 610. Data path 620 can include memory325 (not shown).

In operation, stimulator 200 can deliver a stimulation waveform tostimulate tissue in accordance with a charge setting. Such a chargesetting can be received by receiver 215 and conveyed along data path 620to coulomb counter 610. This conveyance can include the storage of thecharge setting in a memory and the conversion of the charge setting intoa form that is tailored to the operation of coulomb counter 610. Forexample, when the charge setting is an indication that the deliveredcharge should be increased by an incremental step, the magnitude of thecharge to be delivered (rather than the magnitude or existence of theincremental step) can be conveyed to coulomb counter 610.

Meanwhile, a stimulation waveform such as waveform 300 (FIG. 3) can begenerated by waveform generator 605. The stimulation waveform causescharge to be exchanged with the body. This charge passes along thecircuit formed by leads 229, 227, electrodes 205, 207, and the bodyitself. Coulomb counter 610 measures the charge delivered by thestimulation pulses at leads 229, 227. When the charge delivered during astimulation pulse increases above the charge setting, coulomb counter610 outputs an end signal to waveform generator 605 over control line615. The end signal stops the generation of the stimulation pulse, andwaveform generator 605 proceeds with the remainder of the stimulationwaveform.

FIG. 7 is a flowchart of a process 700 by which the flow of chargeduring the electrical stimulation of tissue can be controlled. Process700 can be performed, e.g., by a system for electrically stimulatingtissue, such as system 100 (FIG. 1).

The system performing process 700 receives a charge setting from a userat an external portion at 505. At the external portion, the system canconvert the charge setting into one or more stimulation parameters at705. The conversion of a charge setting into one or more stimulationparameters can be accomplished in a number of ways. Examples arediscussed below, e.g., in FIGS. 10, 11, 12, 17. When system 100 performsprocess 500, processor 130 can convert the charge setting into one ormore stimulation parameters (FIG. 1).

The external portion can then transmit the one or more stimulationparameters to the stimulator at 710. When system 100 performs process500, data transceiver 120 can transmit the one or more stimulationparameters to implanted portion 105 over data link 140 (FIG. 1).

The stimulator can receive the one or more stimulation parameters fromthe external portion at 715. The stimulation parameters can be stored atthe stimulator at 720. When stimulator 200 is part of the system thatperforms process 500, data transceiver 215 can receive the parametersand memory 225 can store the parameters (FIG. 2).

The stimulator can also stimulate in accordance with the one or morestimulation parameters at 725. This generally includes the output ofelectrical waveforms that conform, to some extent, to the stimulationparameters.

FIG. 8 is a flowchart of a process 800 by which the flow of chargeduring the electrical stimulation of tissue can be controlled. Process800 can be performed, e.g., by a system for electrically stimulatingtissue, such as system 100 (FIG. 1).

The system performing process 700 receives a charge setting from a userat an external portion at 505. The received charge setting can betransmitted to a stimulator at 510. The stimulator receives the chargesetting at 515. For example, the charge setting can be transmitted by adata transceiver 120 over a data link 140 to a data transceiver 215 ofan implanted stimulator 200 (FIGS. 1 and 2).

At the stimulator, the system can convert the charge setting into one ormore stimulation parameters at 705. The conversion of a charge settinginto one or more stimulation parameters can be accomplished in a numberof ways, e.g., as discussed below in FIGS. 10, 11, 12, 17. Whenstimulator 200 is included in the system that performs process 500,electrical circuitry 210 can convert the charge setting into one or morestimulation parameters (FIG. 2).

The stimulation parameters can be stored at the stimulator at 720, andthe stimulator can stimulate in accordance with the stimulationparameters at 725. When stimulator 200 is part of the system thatperforms process 500, memory 225 can store the parameters (FIG. 2).

FIG. 9 shows a block diagram of an arrangement of electrical circuitry210 that can convert a charge setting into one or more stimulationparameters. Electrical circuitry 210 includes a charge-to-waveformparameter converter 905, a output/encoder 910, and a waveform generator915. Charge-to-waveform parameter converter 905 implements logic for theconversion of a charge setting into one or more stimulation parameters.The logic can be embodied in and/or implemented by hardware and/orsoftware. Charge-to-waveform parameter converter 905 can thus include adata processor, a memory interface, logic elements, and/or specialpurpose logic circuitry such as one or more FPGA's (field programmablegate arrays) and ASIC's (application specific integrated circuits).

Output/encoder 910 receives one or more stimulation parameters fromcharge-to-waveform parameter converter 905 and outputs them to waveformgenerator 915 in a form that is usable by waveform generator 915 for thegeneration of a stimulation waveform. In general, this use will resultin waveform generator 915 generating waveforms that are in accordancewith the one or more stimulation parameters.

Waveform generator 915 generates a stimulation waveform to stimulatetissue. Waveform generator 915 can be connected to electrodes 205, 207by leads 229, 227 (not shown) to deliver the stimulation waveform.Waveform generator 915 can be programmable in that a stimulation pulseoutput by generator 915 is in accordance with the one or morestimulation parameters received from output/encoder 910.

In operation, decoder/receiver 215 can receive a charge setting over adata link such as data link 140. Decoder/receiver 215 relays the chargesetting to charge-to-waveform parameter converter 905 in a form suitablefor conversion. Converter 905 receives the charge setting and coverts itinto one or more stimulation parameters which are relayed tooutput/encoder 910. Output/encoder 910 programs waveform generator 915with the stimulation parameters. Waveform generator 915 then outputs astimulation waveform across electrodes 205, 207 that is in accordancewith the programming.

FIG. 10 shows a process 1000 for the conversion of a charge setting intoone or more stimulation parameters. Process 1000 can operate ondiscretely or continuously variable charge settings, as discussed below.Process 1000 can be performed in isolation or process 1000 can beperformed as a part of another process. For example, process 1000 can beperformed as a part of processes 700, 800 (FIGS. 7, 8).

If needed, the system performing process 1000 can convert a chargesetting into a charge that is to be delivered at 1005. The exact natureof this conversion will depend on the form of the charge setting. Forexample, when the charge setting is an incremental increase or decreaseof a system-defined setting, the conversion can include determining thecharge that is to be delivered from a look-up table or other memorydevice that associates defined settings with magnitudes of charges to bedelivered. As another example, when the charge setting is a percentincrease in the charge presently delivered, the conversion can includedetermining the new magnitude of the charge to be delivered. As yetanother example, when the charge setting itself is the new magnitude ofthe charge that is to be delivered, no conversion is needed.

The system can divide the charge to be delivered by the current pulseamplitude at 1010 and then set the stimulation pulse duration to thequotient at 1015. For example, when primary pulse amplitude parameter315 characterizes the current amplitude of primary stimulation pulses305 in waveform 300, pulse duration 320 can be approximated by:pulse duration 320≈(pulse amplitude 315)/Q  Equation 3where Q represents the amount of charge to be delivered. As anotherexample, when primary pulse amplitude parameter 315 characterizes thevoltage amplitude of primary stimulation pulses 305 in waveform 300,pulse duration 320 can be approximated by:pulse duration 320≈(Z)(Q)/pulse amplitude 315.  Equation 4where Z represents the impedance and Q represents the amount of chargeto be delivered. Equations 3 and 4 can be adjusted to accommodatevarious forms of pulse amplitude 315 and impedance Z.

In some implementations, pulse amplitude 315 can be maintained at amaximum possible and/or allowable value at all times during stimulation.The maximum value of pulse amplitude 315 can be determined by thephysical constraints of the equipment. The maximum value of pulseamplitude 315 can alternatively be set, e.g., by medical personnel orother users. This setting can take into account the arrangement and/orapplication of the stimulator.

The system performing process 1000 can also calculate (not shown) a newpulse amplitude and a new pulse duration for secondary recovery pulses310. These calculations can yield a balanced-charge biphasic waveform inwhich substantial charge does not, over time, accumulate at theinterface of the stimulating electrode and the body.

FIG. 11 shows a data compilation 1100 for use in the conversion of adiscretely variable charge setting into one or more stimulationparameters. Data compilation 1100 can be stored in a system forelectrically stimulating tissue. For example, data compilation 1100 canbe stored in memory 135 (FIG. 1) and/or in memory 225 (FIG. 2). Thememory that stores compilation 1100 can be non-volatile and programmedusing equipment that is unavailable to non-medical personnel. For thesake of convenience, data compilation 1100 is shown as a table. Othercompilations, including hardwired data storage, ROM data storage, dataobjects, records, files, lists, and multiple compilations that arearranged differently are possible.

Data compilation 1100 includes a charge setting column 1105, astimulation pulse amplitude column 1110, and a stimulation pulseduration column 1115. Stimulation pulse duration column 1115 identifiesone or more discrete stimulation pulse duration values N. Stimulationpulse amplitude column 1110 identifies one or more discrete stimulationpulse amplitude values M. Charge setting column 1105 identifies one ormore discrete stimulation pulse charge setting values. In particular,the number of charge setting values identified in column 1105 is lessthan or equal to the product N*M.

Data compilation 1100 can also identify values of other pulseparameters. For example, data compilation 1100 can identify pulseamplitude values and pulse duration values for secondary recovery pulses310 (not shown). The additional values can yield a balanced-chargebiphasic waveform in which charge does not, over time, accumulate at theinterface of the stimulating electrode and the body.

In operation, a processor, memory interface, or other charge-to-waveformparameter converter can access data compilation 1100 to convert adiscrete charge setting into one or more stimulation parameters. Theconversion can thus be a table look-up or other access of datacompilation 1100 in which a charge setting is used to identify storedwaveform parameters.

FIG. 12 shows a data compilation 1200 for use in the conversion of adiscretely variable charge setting into one or more stimulationparameters. Data compilation 1200 can be stored and represented asdescribed regarding compilation 1100 (FIG. 11) The memory that storescompilation 1200 can be non-volatile and programmed using equipment thatis unavailable to non-medical personnel.

Data compilation 1200 includes charge setting column 1105, stimulationpulse amplitude column 1110, and stimulation pulse duration column 1115.For comparatively low charge settings 1205, 1210, stimulation pulseduration column 1115 includes one or more records 1215 that identifythat the stimulation pulse duration is to be maintained at a “tripduration.” For comparatively high charge settings 1220, 1225,stimulation pulse amplitude column 1110 includes one or more records1230 that identify that the stimulation pulse duration is to bemaintained at a “trip amplitude.”

As illustrated, charge setting column 1105 includes one or moreintermediate charge settings 1235, 1240 where neither the trip amplitudenor the trip duration is identified. However, this need not be the caseand comparatively low charge settings 1205, 1210 can be followeddirectly by comparatively high charge settings 1220, 1225.

FIG. 13 shows waveform 200 with a trip duration 1305 and a tripamplitude 1310. Trip duration 1305 is the shortest possible or allowableduration of a stimulation pulse 205. Trip amplitude 1310 is largestpossible or allowable current or voltage amplitude of a stimulationpulse 205. The illustrated stimulation pulses 205 have a duration 220that exceeds trip duration 1305 and a pulse amplitude 215 that is lessthan trip amplitude 1310. Thus, the charge setting for the illustratedwaveform 200 is one of the intermediate charge settings 1235, 1240.

In some implementations, trip duration 1305 can be between 50 μs lessthan the chronaxie time and 200 μs more than the chronaxie time oftissue to be stimulated. For example, trip duration 1305 can be betweenabout 50 μs and 300 μs, such as about 100 μs. In other implementations,trip duration 1305 can be larger, e.g., up to 500 ms. In someimplementations, trip amplitude 1310 can be the largest amplitude thatthe stimulator can provide. For example, when stimulation waveform 200is shown in terms of current amplitude, is trip amplitude 1310 can beabout 50 mA, or about 10 mA.

In some implementations, data compilation 1200 can indicate that astimulator, for increasing charge settings, is to stimulate at tripduration 1305 with increasing amplitudes 215 until trip amplitude 1310is reached. When trip amplitude 1310 is reached, data compilation 1200can indicate that the stimulator is to stimulate at trip amplitude 1310with increasing pulse durations 220. The charge setting for thistransition between holding pulse duration 220 at trip duration 1305 andholding amplitude 215 at trip amplitude 1310 can be, e.g., about 1000nC.

FIG. 14 shows a process 1400 for controlling charge flow during theelectrical stimulation of tissue. Process 1400 can be performed by asystem for stimulating tissue such as system 100. Process 1400 can beperformed in isolation or process 1400 can be performed as part of alarger process. For example, process 1400 can be performed inconjunction with either of processes 700, 800. In conjunction withprocesses 700, 800, process 1400 can be performed at either the externalportion or the stimulator.

The system performing process 1400 can receive one or more chargeboundaries at 1405. A charge boundary can identify the highest amount ofcharge that is to flow during a stimulation pulse. A second chargeboundary can identify the lowest amount of charge that is to flow duringa stimulation pulse. A charge boundary can reflect the technicalcharacteristics of a stimulator or a charge boundary can reflect a limitset by medical personnel or a device designer to tailor the electricalstimuli to certain ends. Extreme values can be identified either as thevalues themselves (i.e., the maximum value is 5.0) or using comparisons(i.e., the maximum value must be less than 5.0). A charge boundary canbe received from a user such as a medical professional. For example, acharge boundary can be received over a user interface such as userinterface 115 (FIG. 1) and/or input elements 415 of housing 400 ofexternal portion 110 (FIG. 4).

The system can also store the charge boundary at 1410. The chargeboundary can be stored in a memory such as memory 135 of externalportion 110 (FIG. 1) and/or memory 225 of stimulator 200 (FIG. 2).

The system can also receive a charge setting at 1415. The charge settingcan identify a relative change in an amount of charge or the amount ofcharge that is to be delivered during a stimulation pulse. The chargesetting can be received over a user interface such as charge settingcomponents 405 (FIG. 4).

The system can determine if the received charge setting is appropriateat 1420. Determining if the charge setting is appropriate can includecomparing the charge setting to the one or more stored charge boundariesto ensure that the proposed adjustment is within the charge boundaries.

If the system determines that the charge setting is appropriate, thenthe system can adjust one or more stimulation parameter settings inaccordance with the charge setting at 1425. This adjustment can includeconverting the charge setting into one or more stimulation parametersettings as discussed above.

On the other hand, if the system determines that the proposed chargesetting is inappropriate, the system can accommodate the inappropriateadjustment at 1430. For example, an inappropriate charge setting can bediscarded, the user informed of the discard, and operations continuedusing a previous charge setting. As another example, an inappropriatecharge setting can be changed to the violated charge boundary, the userinformed of the change, and one or more stimulation parameter settingscan be adjusted in accordance with the charge boundary.

With a stimulation parameter setting adjusted or an inappropriateadjustment accommodated, the system can determine if changes to thecharge setting are to end at 1435. This determination can be made basedon a number of different factors including user input indicating thatadjustments are to end or a lack of user input over time.

If the system determines that adjustments are indeed to end, then thesystem can stimulate in accordance with the existing stimulationparameter settings at 1440. However, if adjustments are not going toend, then the system can receive an additional charge setting at 1415.

FIG. 15 shows a process 1500 for controlling charge flow during theelectrical stimulation of tissue. Process 1500 can be performed by asystem for stimulating tissue such as system 100. Process 1500 can beperformed in isolation or process 1500 can be performed as part of alarger process. For example, process 1500 can be performed inconjunction with either of processes 700, 800. In conjunction withprocesses 700, 800, process 1500 can be performed at either the externalportion or the stimulator.

The system performing process 1500 can receive one or more stimulationboundaries at 1505. A stimulation boundary is an extreme allowable valueof a stimulation parameter. The stimulation boundaries can identify theextreme allowable value(s) of one or more stimulation parameters, suchas parameters 315, 320, 325, 330, 335, 340, 345 (FIG. 3). Trip duration1305 and trip amplitude 1310 (FIG. 13) are thus stimulation boundaries.A stimulation boundary can reflect the technical characteristics of astimulator or a stimulation boundary can reflect a limit set by medicalpersonnel or a device designer to tailor the electrical stimuli tocertain ends. Extreme values can be identified either as the valuesthemselves (i.e., the maximum value is 5.0) or using comparisons (i.e.,the maximum value must be less than 5.0). The stimulation boundaries canbe received over a user interface such as user interface 115 (FIG. 1).

The system can also store the received stimulation boundaries at 1510.The stimulation boundaries can be stored in memory 135 in externalportion 110 of system 100 (FIG. 1). The stimulation boundaries can alsobe stored in memory 225 in stimulator 200 (FIG. 2).

The system performing process 1500 can also receive a charge setting at1415 and convert the charge setting into one or more waveformstimulation parameters at 705.

The system can also determine if the one or more waveform stimulationparameters are appropriate at 1520. Determining if the stimulationparameters are appropriate can include comparing the stimulationparameters to one or more stored stimulation boundaries to ensure thatthe stimulation parameters are within the stimulation boundaries.

If the system determines that the stimulation parameters areappropriate, then the system can store the appropriate parameters at1525. For example, appropriate stimulation parameters can be stored inmemory 225 in stimulator 200 (FIG. 2).

On the other hand, if the system determines that the stimulationparameters are inappropriate, the system can accommodate theinappropriate stimulation parameters at 1530. For example, aninappropriate stimulation parameter can be discarded, the user informedof the discard, and operations continued using a previous stimulationparameter. As another example, an inappropriate stimulation parametercan be changed to the violated stimulation boundary, the user informedof the change, and operations continued using the changed stimulationparameter. As yet another example, an inappropriate stimulationparameter can be stored as if it were appropriate. However, thestimulation that is actually delivered can be controlled by a devicesuch as a voltage or current limiter that prevents the deliveredstimulation from actually violating the stimulation boundary.

With an appropriate stimulation parameter stored or an inappropriateparameter accommodated, the system can determine if changes to thecharge setting are to end at 1435. If the system determines thatadjustments are indeed to end, then the system can stimulate inaccordance with the existing stimulation parameter settings at 1440.However, if adjustments are not going to end, then the system canreceive an additional charge setting at 1415.

FIG. 16 shows a block diagram of one implementation of a stimulator 200in which charge flow is controlled during stimulation. In addition tocharge-to-waveform parameter converter 905, output/encoder 910, andwaveform generator 915, electrical circuitry 210 includes step-upcircuitry 1610. Step-up circuitry 1610 includes one or more devices thatincreases the potential difference output by power source 220 for use instimulating tissue. In particular, step-up circuitry 1610 outputs ahigher potential difference on lines 1615 to waveform generator 915 thanstep-up circuitry 1610 receives on a supply line 1620 from source 220.Step-up circuitry 1610 can include, e.g., voltage converter circuitry,charge pump circuitry, and the like.

In operation, receiver 215 can receive a charge setting over a data linksuch as data link 140. Receiver 215 relays the charge setting tocharge-to-waveform parameter converter 905. Converter 905 receives thecharge setting and coverts it into one or more stimulation parameterswhich are relayed to output/encoder 910. Output/encoder 910 programswaveform generator 915 with the stimulation parameters.

Output/encoder 910 can program waveform generator 915 with stimulationparameters that call for waveform generator 915 to output a waveformthat includes voltage differences in excess of a supply voltage providedon supply line 1620 by power source 220. In these cases, waveformgenerator 915 can be supplied by step-up circuitry 1610 to generate thevoltage differences in excess of the supply voltage. Waveform generator915 can then output a stimulation waveform across electrodes 205, 207that is in accordance with the programming.

FIG. 17 shows a data compilation 1700 for use in the conversion of adiscretely variable charge setting into one or more stimulationparameters.

Data compilation 1700 is adapted for use with stimulators 200 thatinclude certain classes of step-up circuitry, such as step-up circuitry1610 (FIG. 16). In particular, data compilation 1700 is adapted for usewith stimulators 200 that include classes of step-up circuitry thatgenerate discrete “steps-up” in voltage.

One example of such step-up circuitry is charge pump circuitry thatgenerates one or more discrete voltage steps (at least one of which isin excess of the supply voltage). These voltage steps can be used todefine discrete voltage amplitudes of stimulation or other pulses.Another example of such step-up circuitry is voltage converter circuitrythat outputs one or more discrete voltage steps that are the product ofsupply or other voltages and one or more discrete factors. For example,voltage converter circuitry may be able to generate a discrete voltageof two times the supply voltage. These discrete voltage steps can beused to define discrete voltage amplitudes of stimulation or otherpulses. Yet another example is a combination of step-up circuitry withvoltage converter circuitry. One or more discrete voltage steps outputby step-up circuitry can be input into voltage converter circuitry,where it is multiplied by one or more discrete factors to generatediscrete voltage steps. Such discrete voltage steps can be used todefine discrete voltage amplitudes of stimulation or other pulses.

Data compilation 1700 includes charge setting column 1105, stimulationpulse amplitude column 1110, and stimulation pulse duration column 1115.Stimulation pulse amplitude column 1110 includes groups of two or morerecords 1705, 1710 that identify that the stimulation pulse duration isto be maintained at voltage amplitudes that correspond to the voltagesteps generated by the charge pump circuitry. For example, records 1705identify that the same voltage step 1 (with different durations) is tobe used with two different charges. Similarly, records 1710 identifythat the same voltage step 2 (with different durations) is to be usedwith two different charges.

By setting the stimulation pulse amplitude to about the same level asthe voltage step, the efficiency of the step-up circuitry is increased.In particular, there is no voltage loss associated with a reduction ofthe voltage step to a lower voltage. Rather, the voltage step can beused directly to generate a stimulation pulse.

FIGS. 18, 19, and 20 show another implementation of implanted portion105, namely a stimulator 2800. In particular, FIG. 18 shows a side viewof stimulator 2800, FIG. 19 shows a sectional view of stimulator 2800along the line 19-19 in FIG. 18, and FIG. 20 shows an end view ofstimulator 2800.

Stimulator 2800 includes electrodes 2822 and 2824, a power source 2816,electronic subassembly 2814, and a case 2812. Electrode 2822 is anactive/stimulating electrode whereas electrode 2824 is anindifferent/reference electrode. Electrodes 2822 and 2824 can be madefrom any of the materials discussed above.

Power source 2816 provides power for the operation of stimulator 2800,including the delivery of electrical stimuli to tissue throughelectrodes 2822 and 2824. Power source 2816 can be a primary battery, arechargeable battery, super capacitor, a nuclear battery, a mechanicalresonator, an infrared collector (receiving, e.g., infrared energythrough the skin), a thermally-powered energy source (where, e.g.,memory-shaped alloys exposed to a minimal temperature differencegenerate power), a flexural powered energy source (where a flexiblesection subject to flexural forces is placed in the middle of the long,thin-rod shape of the microstimulator), a bioenergy power source (wherea chemical reaction provides an energy source), a fuel cell (much like abattery, but does not run down or require recharging, but requires onlya fuel), a bioelectrical cell (where two or more electrodes usetissue-generated potentials and currents to capture energy and convertit to useable power), an osmotic pressure pump (where mechanical energyis generated due to fluid ingress), or the like.

When power source 2816 is a battery, it can be a lithium-ion battery orother suitable type of battery. When power source 2816 is a rechargeablebattery, it can be recharged from an external system through a powerlink such as power link 145 (FIG. 1). One type of rechargeable batterythat can be used is disclosed in International Publication WO 01/82398A1, published 1 Nov. 2001, and/or WO 03/005465 A1, published 16 Jan.2003, the contents of both of which are incorporated herein byreference. Other battery construction techniques that can be used tomake power source 2816 include those shown, e.g., in U.S. Pat. Nos.6,280,873; 6,458,171, and U.S. Publications 2001/0046625 A1 and U.S.2001/0053476 A1, the contents of all of which are also incorporatedherein by reference. Recharging can be performed using an externalcharger.

Electronic subassembly 2814 includes a coil 2818 and a stimulatingcapacitor 3015. Electrode 2822 is coupled to electronic subassembly 2814through stimulating capacitor 3015. The coil 2818 can receive power forcharging power source 2816 using power received over power link 145(FIG. 1).

Electronic subassembly 2814 can also include circuitry for stimulation,battery charging (when needed), telemetry, production testing, andbehavioral control. The stimulation circuitry can be further dividedinto components for high voltage generation, stimulation phase currentcontrol, recovery phase current control, charge balance control, andover voltage protection circuitry. The telemetry circuitry can befurther divided into an OOK receiver, FSK receiver, and FSK transmitter.The behavioral control circuitry can be further divided into componentsfor stimulation timing, high voltage generation closed loop control,telemetry packet handling, and battery management. In addition to thesefunctions, there is circuitry for reference voltage and referencecurrent generation, system clock generation, and Power-On Reset (POR)generation.

In operation, charging circuitry within electronic subassembly 2814 candetect the presence of an external charging field. Upon detection,stimulator 2800 can receive a telemetry message and recharge powersource 2816, as necessary. The electronic subassembly 2814 can measure arectified voltage during recharging and transmit the measured voltagevalue to an external device over a data link such as link 140 (FIG. 1).Battery voltage measurements can be made at times when stimulationpulses are not being delivered. U.S. Pat. No. 6,553,263, incorporatedherein by reference, describes charging technology that also can beused.

When power source 2816 used within stimulator 2800 is something otherthan a rechargeable battery, e.g., a primary battery and/or one of thealternative power sources described previously, then the electronicsubassembly 2814 can be modified appropriately to interface with,control and/or monitor whatever power source is used. For example, whenpower source 2816 comprises a primary battery, electronic subassembly2814 can be simplified to include only monitoring circuitry and excludecharging circuitry. Such monitoring circuitry can provide statusinformation regarding how much energy remains stored within the primarybattery to provide the physician and/or patient an indication of theremaining life of the battery.

As another example, when power source 2816 used within stimulator 2800is a super capacitor used in combination with a primary battery and/or arechargeable battery, electronic subassembly 2814 can use the chargestored on the super capacitor to power stimulator 2800 during times ofpeak power demand. Such times include times when telemetry signals arebeing transmitted from stimulator 2800 to one or more externaldevice(s), or when the amplitude of the stimulation pulses has beenprogrammed to be relatively high. When used in combination with arechargeable battery, electronic subassembly 2814 can use the chargestored on the super capacitor to recharge the rechargeable battery or topower stimulator 2800 at times of high power demand.

Electronic subassembly 2814 can also include protection circuitry to actas a failsafe against battery over-voltage. A battery protection circuitcan continuously monitor a battery's voltage and electrically disconnectthe battery if its voltage exceeds a preset value.

Electronic subassembly 2814 can also include a coulomb counter, awaveform generator, a charge-to-waveform parameter converter, anoutput/encoder, a memory, step-up circuitry, a processor and/or otherelectronic circuitry that allow it to generate stimulating pulses thatare applied to a patient through electrodes 2822 and 2824 in accordancewith logic located within the electronic subassembly 2814. The processorand/or other electronic circuitry can also control data communicationwith an external portion such as external portion 110 (FIG. 1). Theprocessor and/or other electronic circuitry can allow stimulator 2800 toperform processes described above in FIGS. 5, 7, 8, 10, 14, 15.

Electronic subassembly 2814 can also include a panel 2802, integratedcircuitry 2806, capacitors 2808, diodes 2810, and two ferrite halves3012. The arrangement of these components in electronic subassembly 2814is described in U.S. Patent Publication No. 2005/0021108, the contentsof which are incorporated herein by reference.

Case 2812 can have a tubular or cylindrical shape with an outer diametergreater than about 3.20 mm and less than about 3.7 mm. For example, case2812 can have an outer diameter of about 3.30 mm. Case 2812 can have aninner diameter that encloses electronic subassembly 2814 of greater thanabout 2.40 mm and less than about 2.54 mm. Case 2812 can have an innerdiameter that encloses power source of greater than about 2.92 mm andless than about 3.05 mm. The length of case 2812 can be less than about30 mm, and less than about 27 mm. The portion of case 2812 that encloseselectronic subassembly 2814 can be less than about 13.00 mm in length.The portion of case 2812 that encloses power source 2816 that enclosespower source 2816 can be about 11.84 mm in length. These dimensions areonly examples and can change to accommodate different types of batteriesor power sources. For example, stimulator 2800, instead of beingcylindrically shaped, can have a rectangular, asymmetrical, or ovoidcross section. Case 2812 can be Magnetic Resonance Imaging (MRI)compatible.

Case 2812 is sealed to protect electrical components inside stimulator2800. For example, case 2812 can be hermetically-sealed and made fromtwo cylindrical cases, namely, a titanium 6/4 case 2813 and a zirconiaceramic case 2815. Other materials and shapes for the housing can alsobe used. A titanium 6/4 or other suitable connector 2836 can be brazedwith a titanium nickel alloy (or other suitable material) to ceramiccase 2815 for securing the mating end of titanium case 2813. A connector2836 has an inside flange 2836A and an outside flange 2836B which serveto “self center” the braze assembly. Before inserting the subassemblyand before securing the mating ends, conductive silicone adhesive 2838can be applied to the inside end of the ceramic shell as well as to theinside end of the titanium shell. A molecular sieve moisture gettermaterial 2835 is also added to areas 2835A, 2835B, and 2835C (FIG. 19)before the brazing process.

The “spiral” self centering button electrode 2822 can be made fromtitanium 6/4 or other suitable material and plated with an iridiumcoating or other suitable conductive coating. An end view of electrode2822 is shown in FIG. 20. A spiral groove 2924 can be made instimulating surface 2922 of the electrode 2822. Other groove shapes,such as a cross hatch pattern or other patterns can also be used toincrease the conductive surface area 2922 of electrode 2822.

The sharp edges in groove 2924 can force a more homogeneous currentdistribution over the surface 2922 and decrease the likelihood ofelectrode corrosion over time by reducing current density along thesharp groove edges. A tool made in the shape of a trapezoid or similarshape can be used to cut the groove 2924 into a spiral or other shape.Other devices for cutting the groove 2924 can be used such as, e.g., ionbeam etching.

The button electrode 2822 can act as active or stimulating electrode. Atitanium/nickel alloy 2840 or other suitable material can be used tobraze the button electrode 2822 to the zirconia ceramic case 2815. Anend view of the stimulator 2800 is shown in FIG. 20 where the end viewof the stimulating “spiral” button electrode 2822 can be seen. The end2842 of the titanium shell 2813 can be plated with an iridium coating(other suitable conductive coating can be applied), which plated areabecomes the indifferent iridium electrode 2824.

FIG. 18 shows a top view of stimulator 2800 with the external coatingsdepicted. A type C parylene or other suitable electrically insulatingcoating can be applied to the shaded area 2844, e.g., by standardmasking and vapor deposition processes. The zirconia ceramic case isleft exposed in area 2848 and the iridium electrode 2824 is shown on theend 2842 of the titanium case 2813.

U.S. Pat. No. 6,582,441, incorporated herein by reference, describes asurgical insertion tool which can be used for implanting stimulator2800. The procedures taught in the '441 patent for using the tool andassociated components can be used for implanting and extractingstimulator 2800. The surgical insertion tool described in the '441patent facilitates the implantation of stimulator 2800 in a patient sothat stimulating electrode 2822 is proximate to a nerve site (e.g., nearthe pudendal nerve for treating patients with urinary urgeincontinence). The distance between electrode 2822 and the nerve sitecan be, for example, less than 1-2 mm.

Other implantation procedures exist relating to the specific area to bestimulated. The stimulator 2800 can also be implanted in other nervesites relating to preventing and/or treating various disordersassociated with, e.g., prolonged inactivity, confinement orimmobilization of one or more muscles and/or as therapy for variouspurposes including paralyzed muscles and limbs, by providing stimulationof the cavernous nerve(s) for an effective therapy for erectile or othersexual dysfunctions, and/or by treating other disorders, e.g.,neurological disorders caused by injury or stroke.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without. Forexample, the described systems and techniques can be applied toelectrical stimulators that are wholly extracorporeal. Otherimplementations are within the scope of the following claims.

1. A method comprising: storing a new charge setting value specifying anamount of charge that is to flow during a stimulation pulse; andgenerating and delivering the stimulation pulse in a manner such that anamount of charge delivered to the tissue during the stimulation pulsehas a value that is substantially equal to the stored charge settingvalue, wherein delivering the stimulation pulse comprises monitoring theflow of charge during delivery of the stimulation pulse, and halting thedelivery based on the flow of charge exceeding the stored charge settingvalue.
 2. The method of claim 1, further comprising generating astimulation waveform that includes the stimulation pulse and a secondarypulse, the secondary pulse to reduce accumulation of charge at anelectrode that has delivered the stimulation pulse.
 3. The method ofclaim 1, further comprising: receiving a charge setting; and derivingthe new charge setting value from the received charge setting.
 4. Themethod of claim 3, wherein the received charge setting is a new chargesetting.
 5. The method of claim 3, wherein the received charge settingis an incremental or decremental charge setting.
 6. The method of claim3, wherein the charge setting is transmitted from an external controldevice to a neurostimulator.
 7. The method of claim 3, wherein thecharge setting is received from a user.
 8. The method of claim 1,wherein delivering the stimulation pulse comprises: changing, based onthe stored charge setting value, one or more stimulation parameters thatcharacterize one or more aspects of a stimulation waveform that includesthe stimulation pulse; and delivering the stimulation waveform inaccordance with the one or more stimulation parameters.
 9. The method ofclaim 8, wherein changing the one or more stimulation parameterscomprises converting the stored charge setting value into the one ormore stimulation parameters.
 10. The method of claim 9, whereinconverting the stored charge setting value comprises calculating astimulation pulse duration using a stimulation pulse amplitude.
 11. Themethod of claim 9, wherein converting the stored charge setting valuecomprises accessing a data compilation using the stored charge settingvalue to identify at least one of a predetermined stimulation pulseduration and predetermined stimulation pulse amplitude.
 12. The methodof claim 1, wherein the new charge setting value is stored in memory.13. A method comprising: storing a new charge setting value specifyingan amount of charge that is to flow during a stimulation pulse; andgenerating and delivering the stimulation pulse in a manner such that anamount of charge delivered to the tissue during the stimulation pulsehas a value that is substantially equal to the stored charge settingvalue, wherein delivering the stimulation pulse comprises converting thestored charge setting value into the one or more stimulation parametersthat characterize one or more aspects of a stimulation waveform thatincludes the stimulation pulse, and delivering the stimulation waveformin accordance with the one or more stimulation parameters, whereinconverting the stored charge setting value into the one or morestimulation parameters, comprises holding a stimulation pulse amplitudesubstantially constant for two or more different charge settings, anddetermining a stimulation pulse duration based on the stored chargesetting value and the substantially constant stimulation pulseamplitude.
 14. The method of claim 13, wherein holding the stimulationpulse amplitude substantially constant comprises accessing a datacompilation that associates a substantially constant stimulation pulseamplitude with the two or more charge settings.
 15. The method of claim13, wherein converting the stored charge setting value into the one ormore stimulation parameters further comprises: holding a stimulationpulse duration substantially constant for another two or more differentcharge settings; and determining a stimulation pulse amplitude based onthe stored charge setting and the substantially constant stimulationpulse duration.
 16. The method of claim 15, wherein: the settings forwhich the stimulation pulse amplitude is held substantially constant arediscrete charge settings that specify relatively smaller amounts ofcharge flow; and the charge settings for which the stimulation pulseduration is held substantially constant are discrete charge settingsthat specify relatively larger amounts of charge flow.
 17. The method ofclaim 16, wherein there are no charge settings intermediate between thecharge settings for which the stimulation pulse amplitude is heldsubstantially constant and the charge settings for which the stimulationpulse duration is held substantially constant.
 18. The method of claim13, wherein holding the stimulation pulse amplitude substantiallyconstant comprises accessing a data compilation that associates each ofa plurality of substantially constant voltage steps with the two or morecharge settings.
 19. A method comprising: determining a new chargesetting value specifying a charge that is to flow during a stimulationpulse that electrically stimulates a tissue; generating and initiatingdelivery of the charge to the tissue during the stimulation pulse;monitoring the flow of the charge during the stimulation pulse; andhalting the delivery of the based on the flow of charge exceeding thenew charge setting value.
 20. The method of claim 19, further comprisinggenerating a stimulation waveform that includes the stimulation pulseand a secondary pulse, the secondary pulse to reduce accumulation ofcharge at an electrode that has delivered the stimulation pulse.
 21. Themethod of claim 19, further comprising: receiving a charge setting; andderiving the new charge setting value from the received charge setting.22. The method of claim 21, wherein the received charge setting is a newcharge setting.
 23. The method of claim 21, wherein the received chargesetting is an incremental or decremental charge setting.
 24. The methodof claim 21, wherein the charge setting is transmitted from an externalcontrol device to a neurostimulator.
 25. The method of claim 21, whereinthe charge setting is received from a user.
 26. A method comprising:determining a new charge setting value specifying a charge that is toflow during a stimulation pulse that electrically stimulates a tissue;converting the new charge setting value into one or more stimulationparameters that characterize one or more aspects of a stimulationwaveform that includes the stimulation pulse, wherein the conversion ofthe new charge setting value into the one or more stimulation parameterscomprises holding a stimulation pulse amplitude substantially constantfor two or more different charge settings, and determining a stimulationpulse duration based on the new charge setting value and thesubstantially constant stimulation pulse amplitude; and generating anddelivering the stimulation waveform in accordance with the one or morestimulation parameters.
 27. The method of claim 26, wherein thestimulation waveform includes a secondary pulse, the secondary pulse toreduce accumulation of charge at an electrode that has delivered thestimulation pulse.
 28. The method of claim 26, further comprising:receiving a charge setting; and deriving the new charge setting valuefrom the received charge setting.
 29. The method of claim 28, whereinthe received charge setting is a new charge setting.
 30. The method ofclaim 28, wherein the received charge setting is an incremental ordecremental charge setting.
 31. The method of claim 28, wherein thecharge setting is transmitted from an external control device to aneurostimulator.
 32. The method of claim 28, wherein the charge settingis received from a user.
 33. The method of claim 26, wherein holding thestimulation pulse amplitude substantially constant comprises accessing adata compilation that associates a substantially constant stimulationpulse amplitude with the two or more charge settings.
 34. The method ofclaim 26, wherein the conversion of the new charge setting value intothe one or more stimulation parameters further comprises holding astimulation pulse duration substantially constant for another two ormore different charge settings, and determining a stimulation pulseamplitude based on the new charge setting value and the substantiallyconstant stimulation pulse duration.
 35. The method of claim 34, whereinthe settings for which the stimulation pulse amplitude is heldsubstantially constant are discrete charge settings that specifyrelatively smaller amounts of charge flow, and the charge settings forwhich the stimulation pulse duration is held substantially constant arediscrete charge settings that specify relatively larger amounts ofcharge flow.
 36. The method of claim 35, wherein there are no chargesettings intermediate between the charge settings for which thestimulation pulse amplitude is held substantially constant and thecharge settings for which the stimulation pulse duration is heldsubstantially constant.
 37. The method of claim 26, wherein holding thestimulation pulse amplitude substantially constant comprises accessing adata compilation that associates each of a plurality of substantiallyconstant voltage steps with the two or more charge settings.
 38. Amethod comprising: determining a new charge setting value specifying acharge that is to flow during a stimulation pulse that electricallystimulates a tissue; converting the new charge setting value into one ormore stimulation parameters that characterize one or more aspects of astimulation waveform that includes the stimulation pulse, wherein theconversion of the new charge setting value into the one or morestimulation parameters comprises holding a stimulation pulse durationsubstantially constant for two or more different charge settings, anddetermining a stimulation pulse amplitude based on the new chargesetting value and the substantially constant stimulation pulse duration;and generating and delivering the stimulation waveform in accordancewith the one or more stimulation parameters.
 39. The method of claim 38,wherein the stimulation waveform includes a secondary pulse, thesecondary pulse to reduce accumulation of charge at an electrode thathas delivered the stimulation pulse.
 40. The method of claim 38, whereinholding the stimulation pulse duration substantially constant comprisesaccessing a data compilation that associates a substantially constantstimulation pulse duration with the two or more charge settings.